I have a 2011 Outback 3.6R, which is mechanically identical to your Legacy, so I will give you both my experience and my advice on this topic.
In an effort to make their vehicles appear to be almost maintenance-free, all car mfrs are in a race to see who can list the least required maintenance in their maintenance schedules. And, for the car owner who sells or trades in his vehicle every 3 or 4 years, these bare-bones, extremely minimal maintenance schedules, will probably not present a problem.
However, for the car owner who intends to keep his vehicle for the long term, and for the vehicle owner who wants flawless performance, it is important to go beyond the ridiculously minimal maintenance requirements that all car mfrs list nowadays.
When I had the 30k service done on my Outback, here is what I had done:
Change air filter
Change brake fluid
Change trans fluid
Change fluid in both differentials
While the “standard” 30k service at the dealership includes changing the cabin air filter, I declined that service as I do that myself every year.
One glaring error in your post is the belief that the brake fluid flush/change is not a required part of Subaru’s maintenance schedule at 30k miles. In reality, it is listed with an “R”, meaning, “replace”, just like the engine air filter. Because brake fluid is hygroscopic (meaning that it absorbs water from the atmosphere), it is very important to change brake fluid on the specified schedule.
In theory, the dealer charged $597 for the services listed above, along with a bunch of “inspections”. In reality, as a result of the dealership’s Senior Citizen discount, plus my use of $500 worth of “Subaru Bucks”, I paid a grand total of $13.12 (including sales tax) for this major service. (I asked the service manager if I held the record for the lowest payment for major services, and he informed me that I did not. He said that another customer had bought tires from them at the time of his 60k service, and that this customer produced enough Subaru Bucks to pay less than $5.00 for that major service and 4 tires.)
If you don’t currently have the Subaru MasterCard (administered by Chase bank), you really should get it, as it pays a 3% rebate on everything that you charge to the card. Every time that you reach the $3,000 plateau of charges, Chase sends you a $100 voucher, which is called a Subaru Buck. These certificates have an expiration date at least 3 years in the future, so you can accumulate them without much fear of them expiring.
I accumulate these certificates, and use them for parts and service, and for my next car purchase. Even though I used $500 worth of those certificates a few months ago for the 30k service, I already have an additional $700 of them stockpiled, so that I will have an equally low cost for my 60k, 90k, & 120k services, and then I can use whatever I have left for my next car purchase. Typically, when I buy a Subaru, I present anywhere from $700 to $1,000 worth of these certificates after I have negotiated my best price, thus getting a very nice discount on the purchase price.
And, please don’t listen to your family members, whose advice (at least on things automotive in nature) is very badly flawed. If you wait until you have transmission problems before you change the fluid, you will very likely not be able to cure those trans problems.
Instead, if you change the trans fluid every 3 yrs/30k miles, you can help to prevent transmission problems. This is the plan that I have followed with all of my cars over the years (including two previous Subarus), and I have never had transmission problems. By contrast, some of my friends (who have beliefs similar to your relatives) have had to overhaul/replace their transmissions at 90k-110k miles. The old saying… “An ounce of prevention is worth a pound of cure”…is very apt when it comes to the very complex device known as an automotive transmission.
If you have any other questions, feel free to ask me.
And, I urge you to get that Subaru MasterCard, as you will be able to have your maintenance done at the dealership (with genuine Subaru fluids) for ridiculously low prices if you get that card and use it for virtually every purchase, as I do.